EXPERIMENT 9 MOISTURE-DENSITY RELATION …

1 Engineering Properties of Soils Based on Laboratory Testing Prof. Krishna Reddy, UIC 91 EXPERIMENT 9 MOISTURE-DENSITY RELATION (COMPACTION) TEST Purpose: This laboratory test is performed to determine the relationship between the moisture content and the dry density of a soil for a specified compactive effort. The compactive effort is the amount of mechanical energy that is applied to the soil mass. Several different methods are used to compact soil in the field, and some examples include tamping, kneading, vibration, and static load compaction.

2 This laboratory will employ the tamping or impact compaction method using the type of equipment and methodology developed by R. R. Proctor in 1933, therefore, the test is also known as the Proctor test. Two types of compaction tests are routinely performed: (1) The Standard Proctor Test, and (2) The Modified Proctor Test. Each of these tests can be performed in three different methods as outlined in the attached Table 1. In the Standard Proctor Test, the soil is compacted by a lb hammer falling a distance of one foot into a soil filled mold.

3 The mold is filled with three equal layers of soil, and each layer is subjected to 25 drops of the hammer. The Modified Proctor Test is identical to the Standard Proctor Test except it employs, a 10 lb hammer falling a distance of 18 inches, and uses five equal layers of soil instead of three. There are two types of compaction molds used for testing. The smaller type is 4 inches in diameter and has a volume of about 1/30 ft3 (944 cm3), and the larger type is 6 inches in diameter and has a volume of about 1 ft3 (2123 cm3). If the larger mold is used each soil layer must receive 56 blows instead of 25 (See Table 1).

4 Engineering Properties of Soils Based on Laboratory Testing Prof. Krishna Reddy, UIC 92 Table 1 Alternative Proctor Test Methods Standard Proctor ASTM 698 Modified Proctor ASTM 1557 Method A Method B Method C Method A Method B Method C Material 20% Retained on Sieve >20% Retained on 20% Retained on 3/8 Sieve >20% Retained on <30% Retained on 3/4 Sieve 20% Retained on Sieve >20% Retained on 20% Retained on 3/8 Sieve >20% Retained on <30% Retained on 3/4 Sieve For test sample, use soil passing Sieve 3/8 Sieve Sieve Sieve 3/8 Sieve Sieve Mold 4 DIA 4 DIA 6 DIA 4 DIA 4 DIA 6 DIA No.

5 Of Layers 3 3 3 5 5 5 No. of blows/layer 25 25 56 25 25 56 Note: Volume of 4 diameter mold = 944 cm3 , Volume of 6 diameter mold = 2123 cm3 (verify these values prior to testing) Engineering Properties of Soils Based on Laboratory Testing Prof. Krishna Reddy, UIC 93 Standard Reference: ASTM D 698 - Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbs/ft3 (600 KN-m/m3)) ASTM D 1557 - Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbs/ft3 (2,700 KN-m/m3)) Significance: Mechanical compaction is one of the most common and cost effective means of stabilizing soils.

6 An extremely important task of geotechnical engineers is the performance and analysis of field control tests to assure that compacted fills are meeting the prescribed design specifications. Design specifications usually state the required density (as a percentage of the maximum density measured in a standard laboratory test), and the water content. In general, most engineering properties, such as the strength, stiffness, resistance to shrinkage, and imperviousness of the soil, will improve by increasing the soil density . The optimum water content is the water content that results in the greatest density for a specified compactive effort.

7 Compacting at water contents higher than (wet of ) the optimum water content results in a relatively dispersed soil structure (parallel particle orientations) that is weaker, more ductile, less pervious, softer, more susceptible to shrinking, and less susceptible to swelling than soil compacted dry of optimum to the same density . The soil compacted lower than (dry of) the optimum water content typically results in a flocculated soil structure (random particle orientations) that has the opposite characteristics of the soil compacted wet of the optimum water content to the same density .

8 Engineering Properties of Soils Based on Laboratory Testing Prof. Krishna Reddy, UIC 94 Equipment: Molds, Manual rammer, Extruder, Balance, Drying oven, Mixing pan, Trowel, #4 sieve, Moisture cans, Graduated cylinder, Straight Edge. Engineering Properties of Soils Based on Laboratory Testing Prof. Krishna Reddy, UIC 95 Engineering Properties of Soils Based on Laboratory Testing Prof. Krishna Reddy, UIC 96 Test Procedure: (1) Depending on the type of mold you are using obtain a sufficient quantity of air-dried soil in large mixing pan.

9 For the 4-inch mold take approximately 10 lbs, and for the 6-inch mold take roughly 15 lbs. Pulverize the soil and run it through the # 4 sieve. (2) Determine the weight of the soil sample as well as the weight of the compaction mold with its base (without the collar) by using the balance and record the weights. (3) Compute the amount of initial water to add by the following method: (a) Assume water content for the first test to be 8 percent. (b) Compute water to add from the following equation: ()1008gramsinmasssoilml)(in addtowater= Where water to add and the soil mass are in grams.

10 Remember that a gram of water is equal to approximately one milliliter of water. (4) Measure out the water, add it to the soil, and then mix it thoroughly into the soil using the trowel until the soil gets a uniform color (See Photos B and C). (5) Assemble the compaction mold to the base, place some soil in the mold and compact the soil in the number of equal layers specified by the type of compaction method employed (See Photos D and E). The number of drops of the rammer per layer is also dependent upon the type of mold used (See Table 1).